Polyacetal resin is used in diverse fields as an engineering plastic due to its excellent physical properties, such as mechanical, electrical and chemical properties (e.g., chemical and heat resistances). However, the identification of new end-use applications for polyacetal resins often requires further property alterations and/or enhancements.
One such property that is needed when polyacetal resin is employed to form molded parts used for automotive trim or optical instruments is a relatively low surface gloss. A low surface gloss will thus reduce the light reflectivity property of the molded part. As a result, low surface gloss on molded parts will tend to cause less eye irritation (i.e., since less light will be reflected from the part's surface). Furthermore, low surface gloss on molded parts fabricated from engineering plastics tends to impart a more aesthetically pleasing high-grade appearance to the part.
An ability to "engineer" the surface gloss characteristics would also be beneficial in instances where molded parts fabricated from polyacetal resin (which inherently exhibits a relatively high surface gloss) are used in cooperation with molded pairs formed of other non-polyacetal resins. That is, it would be especially desirable to reduce the surface gloss of polyacetal resin to an extent where it is substantially equivalent to the molded parts of non-polyacetal resin in which it is cooperatively used. An inability to date to reduce the surface gloss of polyacetal resins by controlled amounts so that it is visually imperceptible with parts molded from non-polyacetal resins has thus been one barrier to using polyacetal resin in end-use applications (e.g., as parts for electric and electronic devices) where the polyacetal part will be visible.
Attempts in the past to reduce the inherently high surface gloss of polyacetal resins have included incorporating inorganic filler material, such as calcium carbonate or talc, in a polyacetal base resin. However, large amounts of such inorganic filler material must typically be added to the polyacetal base resin before the desired low surface gloss appearance is realized. The addition of relatively large amounts of inorganic filler material, however, is disadvantageous since it has a tendency to reduce the mechanical characteristics (especially elongation and toughness) normally associated with polyacetal resins. Thus, for example, the mechanical properties may be degraded by the addition of relatively large amounts of filler material to the point where molded parts of such a highly filler-loaded polyacetal resin break during assembly or when dropped.
Another technique to reduce the surface gloss of molded articles has been attempted whereby the surfaces of a mold have been texturized ( i.e. "grained") so that the texture is transferred to the surface of the molded article. In the specific case of polyacetal resins, however, due to their relatively high crystallinity, satisfactory reduction in surface gloss by graining has not been achieved.
Accordingly, what has been needed in this art are polyacetal resin compositions which exhibit their inherent desirable mechanical and physical properties while also having reduced surface gloss characteristics. It is toward providing such polyacetal resin compositions that the present invention is directed.
Broadly, the present invention relates to polyacetal resin compositions having reduced surface gloss characteristics by blending with a polyacetal base resin, a specific polyester resin and a specific isocyanate compound. More particularly, the present invention is directed to novel polyacetal resin compositions which include (A) 100 parts by weight of a polyacetal base resin, (B) between 1 to 50 parts by weight of a polyalkylene terephthalate copolymer having a melt flow temperature of 210.degree. C. or below, and (C) between 0.1 to 10 parts by weight of an isocyanate or isothiocyanate compound, or modifications thereof. Molded articles formed of such compositions exhibit desirable reduced surface gloss characteristics.
Further aspects and advantages of this invention will become more clear after careful consideration is given to the detailed description of the preferred exemplary embodiments thereof which follow.